MRI (magnetic resonance imaging) or X-ray CT (X-ray computerised tomography) can be used both to provide sectional views of a body in real-time and to generate volumetric data (i.e. 3D data) corresponding to a body for later interrogation. Often the volumetric data is interrogated to provide displayable sectional views of the body.
The sectional view can be generated anywhere within the volumetric data. Indeed, some systems give the user a sensation that the sectional view can be freely moved (or “navigated”) through the volumetric data. However, navigating the sectional view through the volumetric data can prove difficult and disorientating to a user.
For example, in conventional MRI or CT systems, graphical user interface (GUI) interactions allow the user to adjust one or more parameters of the sectional view to navigate the sectional view through the volumetric data. Conventional techniques of adjustment often employ mouse and GUI based methods for determining the location of the image plane containing the sectional view. Examples of techniques include: line drawing (Kerr A B et al., Magn Reson Med 1997; 38; p. 355-367); placing points (Debbins J P et al., Magn Reson Med 1996; 36; p. 588-595); and selecting reference icons (Hardy C J et al., Magn Reson Med 1998; 40; p. 105-111). However, the need for the user to manually adjust these parameters often distracts attention from the displayed sectional view of the volumetric data. This is undesirable when interrogating sectional views of MRI or CT generated volumetric data of e.g. a human subject's body, because abnormalities in the subject's anatomy can easily be overlooked.
In an attempt to overcome the need for the user to divert attention away from the displayed sectional view towards the one or more parameter adjustment GUIs, specialized controllers have been proposed, which allow the user generally to remain focussed on the output image. Such controllers typically provide 6 degrees of freedom (DOF) of image plane control so that the corresponding sectional view remains freely navigatable through the volumetric data. Examples of the 6 DOF controllers are the “spaceball” (Hardy C J, et al. Magn Reson Med 1998; 40; p. 105-111), the 3 DOF and 6 DOF mice (Hardy C J, et al. Magn Reson Med 1998; 40; p. 105-111) and the robotic arm (Yi D, et al., Medical Image Computing and Computer-Assisted Intervention MICCAI 2004, vol. 3217, pp. 430-437, 2004).
However, these controllers can rapidly disorientate the user because the image plane (in which the displayed sectional view is generated) is freely movable through the volumetric data. Consequently, a user may have to re-orientate himself in the volumetric data by re-starting the navigation of the image plane from a known location in a known orientation.
It has been proposed that the relative position of the freely movable image plane, in which the sectional view is generated, should be mapped on the volumetric data itself and displayed to the user, thereby providing visual feedback to the user as to the relative position of the image plane with respect to the volumetric data (Hardy C J, et al. Magn Reson Med 1998; 40; p. 105-111 and Stainsby et al., PROC ISMRM 2004: 537). Such feedback is sometimes referred to as image plane tracking. However, the visual feedback still requires the operator to divert attention from the displayed sectional view(s) in order to determine the location of the image plane with respect to the volumetric data. This again creates user distraction, which is undesirable.
The above discussion is mainly directed at the interrogation of volumetric image data. However, the problems associated with navigating volumetric image data using the conventional methods and systems also exist when interrogating a body in real-time, e.g. by MRI or X-ray CT.
WO2008/084232 proposes a method of interrogating volumetric data including the steps of: (i) defining a reference surface relative to the volumetric data; (ii) providing an interrogation window lying in a movable interrogation plane intersecting the reference surface and the interrogation window intersecting the volumetric data, wherein translation and/or rotation of the interrogation plane provides a corresponding movement of the interrogation window; (iii) the interrogation plane being associated with a pole about which pole said interrogation plane is rotatable, and for each movement of the interrogation plane, determining the point of intersection of the pole and the reference surface, determining the relative angle of rotation of the interrogation plane about the pole and determining the angle of inclination of the pole to the reference surface; and (iv) on the basis of the determinations in step (iii), providing a sectional image through the volumetric data corresponding to the position of the interrogation window within the volumetric data. WO2008/084232 also proposes a corresponding method of controlling an imaging apparatus to acquire a sectional image of a body.
The approach of WO2008/084232 is based on an appreciation that that the different diagnostic field of real-time 2D ultrasound scanning has important features lacking in conventional computer implemented data interrogation methods and control systems. Thus, in real-time 2D ultrasound scanning, a sectional view of an appropriate subject can be generated and the image plane (containing the sectional view) can be moved freely through the body. However, here the sonographer uses a combination of their knowledge of the subject's internal anatomy and of tactile and spatial cues from the hand manipulating the ultrasound transducer to move the image plane in a controllable, predictable and “automatic” or intuitive way. The sonographer can therefore focus on the sectional view of the subject provided on a display. It is not necessary to use other means, such as mouse/controller/GUIs, in order to establish where the image plane is located in the subject, i.e. image plane tracking feedback is not required. Further discussion of the approach is provided in Graves M J, et al., Radiology 2009; 252; p. 218-224.
WO2008/084232 and Graves M J, et al., Radiology 2009; 252; p. 218-224 propose prototype controllers for maneuvring the interrogation plane with respect to the reference surface. However, these controllers are bulky and/or relatively complicated which may hinder their widespread uptake and consequently the adoption of the methods of WO2008/084232.